Cationic polymerization is one of the important processes for synthesizing polymer materials. Homopolymers of isoolefin monomers (e.g. isobutene), copolymers of isoolefins with isoprene (e.g. butyl rubber) and copolymers of isoolefins and vinyl aromatic compounds (styrene or derivatives thereof) (e.g. copolymers of isobutene and p-methylstyrene) are the most primary industrial products via cationic polymerization and have a great market demand. Since trace of impurities have an extremely great effect on the cationic polymerization process, the polymerization needs to be conducted under the conditions of almost no oxygen, no water and protection with high purity inert gases and by the technological process of slurry polymerization and solution polymerization. Taking the industrial production of butyl rubber by slurry polymerization process as an example, the polymerization needs to be conducted in the reaction medium of dry chloroalkane at a temperature as low as −100° C. The raw materials, such as isobutene, isoprene and chloroalkane (e.g. methyl chloride) cannot be used unless they are strictly refined and dried. After polymerization, methyl chloride, unreacted monomeric isobutene and isoprene need to be isolated and recovered, and then further strictly refined and dried. Moreover, HCl is produced from methyl chloride during the post-treatment, which results in the apparent corrosion of the equipment. In the production of butyl rubber by the cationic solution polymerization, the heat and mass transfer are difficult since solution viscosity increases remarkably with decreasing polymerization temperature. Thus the monomer conversion has to be controlled under 20%-30%. As a result, the production efficiency is low and the product quality is difficult to be improved and controlled. A great deal of solvents need to be recovered and refined, and the solvent recovery equipment, rectifying unit and drying system having a high processing capacity need to be constructed correspondingly. Meanwhile, the water and oxygen content in the polymerization system should be necessarily and strictly controlled to be several ppm or even lower to synthesize butyl rubber with high molecular weight. Thus the current technological procedures for preparing isoolefin polymers (e.g. butyl rubber) by cationic polymerization are complicated, have strict requirements on the equipment and raw materials and have a high production cost. The current similar cationic polymerization system uses organic solvents as the reaction medium, and requires that the water content therein is lower than several ppm. In the current industrial production of cationic polymerization, the conventional cationic polymerization processes and corresponding continuous polymerization technological procedures require extremely strict dehydration and deoxygenation procedures, to enable the polymerization system and raw materials to achieve the rigor reaction conditions of almost no oxygen and no water, and need to be conducted under the protection of high purity inert gases. It enables the polymerization process and procedures to be extremely complicated and results in rigor requirements on the operation conditions, high equipment investment, high production cost, great technical difficulties and many chemical process units.
During the preparation of butyl rubber, the effect of heat transfer of organic solvents is relatively low. Particularly for the solution polymerization system having a high viscosity, a great deal of instant reaction heat can not be effectively removed in a short period of time unless there is a plurality of ethylene evaporating capacities. Then, it requires a complex reactor and a great ethylene refrigerant circulation, so as to enable the refrigeration system to be bulky and complex. CN101423579A further discloses a system and process in which the cold energy of liquefied natural gas (LNG) having a low temperature (a pressure of 0.1-10 MPa and a temperature of −162° C.˜−150° C.) is used for synthesis of butyl rubber. However, the refrigeration system is complex, and is difficult to be adjusted and controlled.
If water is used as the environmentally-friendly reaction medium for cationic polymerization, it may simplify the polymerization and production process, the equipments and reaction conditions, reduce the production cost and improve the heat and mass transfer. Therefore, it is significant to use an aqueous medium as the reaction medium for the cationic polymerization.
There has been a growing interesting recently in the cationic polymerization using water as the reaction medium. However, the prior art of vinyl monomer cationic polymerization in the aqueous reaction medium is faced with many problems, such as high cost of initiating system, complex technological process, low polymerization efficiency, low molecular weight of resulted polymer products and the like. Moreover, these Lewis acids which have a high cost or are prepared specially are required as co-initiators. These problems in the prior art may refer to WO2004094481A2, WO2004094486A1, JP10130315, JP11080221, “Cationic Polymerization of styrene in Solution and Aqueous Suspension Using B(C6F5)3 as a Water-Tolerant Lewis Acid” (Kostjuk S. V. and Ganachaud F., Macromolecules, vol. 39), “Controlled/living cationic polymerization of styrene with BF3.OEt2 as a coinitiator in the presence of water: Improvements and limitations” (Radchenko A. V., Kostjuk S. V. and Vasilenko I. V., et al, European Polymer Journal, Vol. 43, 2007), “Controlled Cationic Polymerization of Cyclopentadiene with B(C6F5)3 as a Coinitiator in the Presence of Water” (Kostjuk S. V., Radchenko A. V. and Ganachaud F., Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 46, 2008). Thus the development of a new initiating system having a high activity, low cost, commercially obtainable raw materials and being easy and convenient to be used in a polymerization process are the key points for solving the problems in cationic polymerization in aqueous medium in the prior art, and can create conditions for simplifying the technological process, increasing the polymerization efficiency, synthesizing high molecular weight polymer products, reducing the cost and the like. However, the technologies and procedures of the cationic polymerization of the cationic-polymerizable monomers co-initiated directly by Lewis acid such as AlCl3, AlRCl2, BF3, TiCl4, FeCl3, SnCl4, ZnCl2 and the like in the aqueous medium or even in a reaction medium which is totally water have not been reported yet.